1. Field of the Invention
The present invention relates to a power transmission in vehicles such as two-wheeled or three-wheeled motorcycles.
2. Description of the Prior Art
Vehicles such as a two-wheeled motorcycles in which a swing arm for journaling a driving wheel is pivotally supported to a body frame are known to employ the driving wheel coupled to the output member of a power plant through a continuous loop transmission mechanism. The fulcrum of the swing arm and the center of rotation of the drive wheel of such vehicles are known to be disposed concentrically to eliminate any slack in the endless transmission belt of the transmission mechanism during swinging motion of the swing arm. Such a device is disclosed in Japanese Utility Model Publication Kokoku No. 28759/1979, for example.
In such conventionally known motorcycles, the pivot shaft of the swing arm and the drive system of the continuous loop transmission mechanism are separately constructed. In such a device it is not only difficult to accurately bring the pivot fulcrum of the swing arm into coincidence with the center of drive wheel of the continuous loop transmission mechanism, but it is necessary to rigidly form the pivot shaft of the swing arm, to which relatively large loads such as an impact load are applied. This can cause an increase in the weight of the vehicle.
In addition, since it is necessary to associate the output member of a power plant with the drive wheel of a continuous loop transmission mechanism, the output member must extend backward to the vicinity of the swing arm. Thus, the area for installing a rear cushion for suspending the swing arm to the body frame is disadvantageously limited.